The invention relates generally to formation of structures by joining together two opposing substrates, generally of similar geometry, and to methods to affix one to the another so that any additional material in contact with the structure remains unaffected both during and after assembly and sealing processes. A principal application of the invention is the formation of liquid crystal display panels, wherein a quantity of liquid crystal material is sealed between a pair of opposing substrates (e.g. flat glass panels).
The structure may, for example, encapsulate a second material such as a liquid or solid (e.g. liquid crystal material), by joining the pair of structures with a sealant. When the second material is temperature sensitive, the sealant must be such that it or cures or cross links at or near ambient temperature. In particular, this invention focuses in the main on the assembly of flat panel displays. In this preferred utilization, the liquid crystal of the display is contained within a central region of one substrate of the panel assembly before the plate is affixed by a fillet of sealant to the second substrate with the liquid held in place by a peripheral dam or wall. Affixing the second plate to the first causes the liquid crystal to be encapsulated within the display panel assembly, the assembly held together with a sealant applied at the peripheral region of a substrate. For example, the dam may also act as the sealant. Both the dam and the sealant should preferably comprise materials that do not contaminate the liquid crystal at any time.
A preferred method of assembly of flat panel displays entails the use of the xe2x80x9cone drop techniquexe2x80x9d described in U.S. Pat. No. 5,263,888 issued on Nov. 23, 1993 to Teruhisa Ishihara et al. Another method that utilizes filling of one panel plate with liquid crystal prior to assembly with the second panel has been described by von Gutfeld in U.S. patent application Ser. No. 09/197,004, filed Nov. 20, 1998. However, in both cited cases there still exists the problem of containing the liquid crystal material by a non-contaminating peripheral dam wall during filling and attachment to the second plate. Prior to the plate assembly, the dam wall must be somewhat higher than the final level of the liquid crystal material. Therefore, the dam must ultimately have the following properties: 1) be compressible to conform to the appropriate assembled display plate separation, 2) consist of a material that does not interact substantially with the liquid crystal material both during filling of the panel and after assembly and 3) the dam as well as the edge sealant must cure at a temperature or in a manner that does not damage the liquid crystal. Although, in many cases, uv (ultraviolet)-setting epoxy is presently being used to form the dam wall and serve as the sealant, there are problems caused by components of these epoxies leaching into the liquid crystal and thus causing panel performance problems.
In addition, there are regions of the peripheral seal that are not accessible by the uv radiation. Therefore, there may remain some regions that are not fully cured and thus give rise to long term liquid crystal contamination, causing certain peripheral pixels of the display to fail.
The main object of this invention is to provide means for sealing together two opposing substrates with a quantity of a second material (e.g. liquid crystal) encapsulated between them, without physical or chemical damage to the encapsulated material. The invention provides different methods for enhancing the curing or setting of sealants such as epoxies without damaging the encapsulated material.
Broadly, the present invention provides a method of forming a liquid crystal (xe2x80x9cLCxe2x80x9d) display panel by joining a first substrate to a second substrate, each substrate having a central region surrounded by a peripheral region, said method comprising the steps of:
a) depositing a fillet of settable epoxy sealant material in a continuous loop on a peripheral region of said first substrate to surround the central region thereof,
b) depositing a selected quantity of liquid crystal material in a central region of one of said first substrate and said second substrate,
c) placing said second substrate with the peripheral region thereof disposed over the peripheral region of said first substrate and in continuous contact with said fillet along the entire length thereof, and
d) causing setting of the aforesaid fillet of epoxy sealant material to hermetically seal said LC material between said first substrate to said second substrate .
According to a preferred embodiment, step (d) comprises vibrating the first and second substrates to enhance setting of the aforesaid epoxy sealant material, as by curing, cross-linking, or the like.
Alternatively, step (d) may be carried out by scanning along the aforesaid continuous loop of the aforesaid fillet with a focussed beam of a laser (of an ultraviolet, visible, or infrared characteristic wavelength range) to enhance setting (by curing or cross-linking) of the epoxy sealant material, preferably along a peripheral edge of the LC panel. Instead of scanning, a stationary laser (e.g. a pulsed excimer uv laser) may be used to irradiate a linear segment of the fillet of sealant material.
According to a preferred embodiment, step (d) may comprise a step of irradiating the fillet of epoxy sealant material with infrared radiation through a mask that shields the LC material.
While single-component epoxy sealant materials may be used, according to another preferred embodiment, the epoxy sealant material comprises two components, while step (a) comprises depositing fillets of said two components on the peripheral regions of the respective first and second substrates. In this case, step (d) preferably comprises vibrating the first and second substrates to enhance interdiffusion between the aforesaid two components of epoxy sealant material, as by moving an ultrasonic transducer along the continuous loop of the aforesaid fillet of epoxy sealant material.
According to another embodiment, the aforeaid fillet has an aperture to permit escape of a portion of said LC material, and the aperture is sealed with a plug of settable epoxy material, and then the plug is irradiated with a focussed beam of a laser to cure said plug.
According to yet another preferred embodiment, a barrier fillet is deposited in a continuous loop between the LC material and the fillet of epoxy sealant material to prevent contact between the LC material and said epoxy sealant material.